1. Technical Field
This invention relates, in general, to the design and production of semiconductor microchips. More particularly, this invention relates to methods for electrically connecting the various components of a semiconductor microchip.
2. Background Art
The advent of the microchip has revolutionized life in the latter half of the 20th century. Microchips are a ubiquitous part of life, being found in everything from computers to garage door openers. Over the years, the microelectronics industry has diligently sought to further reduce the size of the microelectronics built on silicon chips.
One of the major factors in determining the degree of miniaturization possible on a chip is the amount and type of connections required between the electrical devices contained on the chip. One approach has been to provide a "separate contact" where devices on a chip are electrically connected by the deposition and etching of metals or other conductors between the devices to be connected. One example of this approach is the "damascene" process. According to the damascene process, "troughs" are etched in the silicon dioxide between circuit devices. The entire surface of the chip is then covered with copper or aluminum. Next, the copper is planarized, removing it from the chip's surface and leaving copper only in the troughs. The remaining lines of copper are referred to as "wires" and electrically connect some or all of the devices on a layer of a chip. An example of this is shown in FIG. 23, where two contact vias 2300 are formed that connect the gate to the source/drain diffusion through the interconnect wiring.
The other approach to electrically connecting devices on a chip is to use a "buried contact". A buried contact uses selective doping and diffusion of impurities in the silicon of a chip to provide an electrical connection between the devices on a chip through doped silicon. A buried contract is typically used to electrically connect a device to a nearby region of doped silicon. An example of this is shown in FIG. 24, where the diffusion region 2400 forms a buried contact between a gate conductor and the source/drain diffusion. This of course requires the selective removal of the gate oxide which can lead to processing difficulties.
Both separate contacts and buried contacts present problems to chip design and manufacturing. Using separate contacts made from metals or other conductors to connect devices on a chip requires the additional steps of deposition and etching to establish the proper pattern of connections. Using separate contacts also increases the size of the chip, as there must be enough room on the chip to contain the conducting traces and the connections. By using a traditional buried contact to electrically connect the various devices on a microchip a higher density chip can be manufactured. However, the buried contacts sometimes fail to produce predictable low resistive contacts. Also, a traditional buried contact often encounters current leakage from the buried contact to the chip substrate.
Accordingly, the need exists for a new type of low resistive contact that allows for more compact chip design while avoiding excessive current leakage that is built by relatively simple processing.